The types of light sources used in exposure apparatus for manufacturing semiconductors include g-rays with a wavelength of 436 nm, i-rays with a wavelength of 365 nm, KrF lasers with a wavelength of 248 nm, and ArF lasers with the wavelength of 193 nm, for example. These technologies have evolved to use increasingly shorter wavelengths of light, and extreme ultraviolet (EUV) lithography, which uses extreme ultraviolet (EUV) light with wavelengths near 13.5 nm, has been developed to make it possible to transfer even smaller patterns. In EUV lithography, reflective masks are used instead of transmissive masks because there are few materials that are transparent to EUV light. The reflective masks have a basic structure in which a multilayer reflective film that reflects exposure light is formed on a substrate with low thermal expansion, and a desired transfer pattern is formed on top of a protective film which is for protecting the multilayer reflective film.
Transfer patterns typically take the form of phase shift films (half-tone phase shift type) that reflect a fixed amount of EUV light or the form of absorber films (binary type) that exhibit a relatively strong absorption of EUV light. However, even the absorber films (which absorb a large amount of EUV light and generate a relatively small reflected light) will reflect approximately 0.5% of the EUV light. Therefore, when EUV reflective masks are formed, regardless of whether the phase shift films or the absorber films are used, dedicated light-shielding bands must be formed in order to sufficiently reduce the effects of the reflection of exposure light that is generated adjacently. Here, the “light-shielding bands” refers to a light-shielding frame (region) that is formed so as to surround circuit pattern regions of the mask in order to prevent exposure light from leaking into regions adjacent to a block on a wafer to which a pattern is to be transferred (such as the circuit pattern regions where the pattern is to be transferred). If this light-shielding band does not make it possible to sufficiently reduce the amount of reflected light, the exposure light leaks into the adjacent regions. This can cause a decrease in the resolution of the patterns in the adjacent regions or a decrease in the precision of the transfer size, thereby resulting in a reason for a decrease in yield rate. When the light-shielding band is formed simply using the phase shift film or the absorber film in EUV reflective mask, there is a large amount of reflected light, and this can cause the problems described above. Therefore, a light-shielding band with sufficient light-shielding properties (sufficient reflection-reducing properties) must be used. One representative example of a light-shielding band for an EUV lithography reflective mask is an etched light-shielding band where a portion of a multilayer reflective film which is to be the light-shielding band is etched (hereinafter, simply referred to be as “multilayer reflective film-etched light-shielding band”). This configuration is more advantageous than a multilayer absorber film-type light-shielding band in which additional absorber films for the light-shielding band are layered onto the absorber film used for a transfer pattern in terms of forming transfer patterns with higher precision, reducing occurrence of defects, and preventing the shadowing effects exhibited by multilayer light-shielding band films.
Patent Documents 1 to 4 disclose technologies related to reflective masks for EUV lithography and mask blanks for manufacturing the reflective masks. Patent Document 1 also discloses a light-shielding band and the shadowing effect.